Arsene Wenger has revealed that stats play an important role in determining which of his Arsenal players are substituted.

Wenger is renowned for being a manager who bides his time over substitutions, sometimes to the frustration of Arsenal's supporters.

But the Frenchman has now spoken of the science behind the decisions he takes while watching a match progress from his technical area, reports Football.London.

Speaking to the Arsenal magazine , Wenger said: "We know the players’ physical qualities and who we expect to drop in the second half or not. Nobody’s tired enough at half time to be substituted for that, but in the second half you’ll see that sometimes this player will drop in the last 20 minutes.

"We have a fatigue factor coming in at different levels for everybody and we know the players who drop more in the second half than others. Some remain completely consistent and some even push upwards in the second half.

"There are players who drop up to 15 per cent in the second half, so you have to consider that in your substitutions. Even if you do make substitutions, you always try to keep one free because you know this guy could need to be substituted as well so you need to keep a place for him."

Wenger has been criticised by fans this season for consistently taking off Alexandre Lacazette midway through the second half of games.

Having arrived from Lyon in the summer for what was then a club record fee, many expected the France striker to be a mainstay in the Arsenal attack.

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But having completed the full 90 minutes on his league debut against Leicester on the opening day of the Premier League season, he had to wait until the 3-3 draw against Liverpool on December 22 to do so again.

In all he has stayed on the pitch for the entirety of a Premier League game six times in his Arsenal career - and Wenger has explained why.

The Arsenal boss said: ”I must say that [Lacazette] plays in a position where you sub more than say a defender," Wenger added. "You substitute a striker more than you would a defender, because they always have to provoke, to defend, to attack, you have to create holes in the defences. The strikers are more subbed than others.

"Secondly, he was in an adaptation period where I felt that, without any objective measurement, that sometimes he struggled a bit more in the second part of the game, especially in the last 20 minutes, to create the movement he can.

"I put that down to an adaptation period. It was not so much physically - that didn’t drop so much - it just looked like he was a bit less sharp.”